Transmission mechanism of image scanner with adjustable resolution

1. A method, comprising: switching between a first and a second transmission states in response to a command for changing a moving speed of a carriage via a transmission control set; receiving transmission power from said transmission control set in the first transmission state via a first transmission set; receiving transmission power from said transmission control set in the second transmission state via a second transmission set; synchronously rotating an active gear of said transmission control set with a shaft of a step motor; engaging two follower gears of said transmission control set with said active gear for transmission by said active gear; swinging a swing arm between a first position to allow said follower gears to engage with said first transmission set and a second position to allow said follower gears to engage with said second transmission set; holding said swing arm via a holder of said transmission control set to fix the transmission control set in one of the first and second transmission states to allow said carriage to move at said selected speed; and retracting said holder to release said swing arm in order to change said moving speed of said carriage, and protracting said holder to confine said swing arm in one of the first and second positions in order to fix the transmission control set in one of the first and second transmission states for said scanning operation during rotation of the step motor in both clockwise and counter clockwise directions.

2. The method according to claim 1 , further comprising: swinging said swing arm to said first position in response to a first rotating direction of said shaft of said step motor; and swinging said swing arm to said second position in response to a second rotating direction of said shaft opposite to said first rotating direction.

3. The method according to claim 1 , further comprising: moving said carriage via a common gear of said first and second transmission sets.

4. An apparatus, comprising: a transmission control means for switching between a first and a second transmission states in response to a command for changing a moving speed of a carriage; a first transmission means for receiving transmission power from said transmission control means in the first transmission state; a second transmission means for receiving transmission power from said transmission control means in the second transmission state; wherein said transmission control means comprises an active means for synchronously rotating with a shaft of a step motor; two follower means for engaging with said active means for transmission by said active means; a swing means for swinging between a first position to allow said follower means to engage with said first transmission means and a second position to allow said follower means to engage with said second transmission means; a holder means for selectively holding said swing means to fix the swing means in one of the first and second transmission states to allow said carriage to move at said selected speed; and means for retracting said holder means to release said swing means in order to change said moving speed of said carriage, and means for protracting said holder means to confine said swing means in order to fix the swing means in one of the first and second transmission states for a back and forth scanning operation.

5. The apparatus according to claim 4 , wherein said first and second gears means comprise a common means for moving said carriage via a cyclic belt.

6. A scanner comprising: a first gear set coupled to a common transmission gear; a second gear set coupled to the common transmission gear; a drive gear coupled to a motor; a cyclic belt coupled to the common transmission gear to be driven thereby; a carriage comprising an image sensor mounted to the cyclic belt; a swing arm pivotally mounted concentric with the drive gear; a transmission gear set secured to the swing arm and meshed with the drive gear; and a holder selectively engaged with the swing arm to retain the swing arm in either a first or second position for both forward and backward movement of the carriage, the transmission gear set meshed with the first gear set in the first position and meshed with the second gear set in the second position.

7. The scanner of claim 6 , further comprising an actuator having a locked position and a unlocked position, the actuator positioning the holder to hinder movement of the swing arm in the locked position and permitting movement of the swing arm between the first and second positions in the unlocked position.

8. The scanner of claim 6 , wherein the transmission gear set comprises first and second gears meshed with one another, the first gear meshed with the drive gear and the second gear selectively meshed with the first and second gear sets.

9. The scanner of claim 6 , wherein common transmission gear is coupled to the drive belt.

10. A method comprising: disengaging a holder from a swing arm having a transmission gear set secured thereto, the swing arm pivotable concentrically with rotation of a drive gear meshed with the transmission gear set; actuating the drive gear such that the drive gear urges the swing arm from a first position to a second position, the transmission gear set meshed with a first gear set in the first position and meshed with a second gear set in the second position, the first and second gear sets coupled to a common transmission gear; and reengaging the holder with the swing arm such that the swing arm is retained in the second position for both clockwise and counterclockwise rotation of the drive gear.

11. The method of claim 10 , further comprising: again disengaging the holder from the swing arm; actuating the drive gear such that the drive gear urges the swing arm from the second position to the first position; and again reengaging the holder to retain the swing arm in the first position.

12. The method of claim 10 , wherein disengaging the holder from the swing arm comprises actuating an electromagnetic valve.

13. The method of claim 10 , further comprising actuating the drive gear to transmit movement to the common transmission gear.

14. The method of claim 13 , wherein the common transmission gear is coupled to a drive belt.

15. The method of claim 14 , wherein the drive belt has a scanning module coupled thereto.

16. A transmission device comprising: a first means for transmitting coupled to a common transmission gear; a second means for transmitting coupled to the common transmission gear; a means for driving coupled to a motor; a means for rotating; a third means for transmitting mounted to the means for rotating and engaged with the means for driving; and a means for retaining the means for rotating in both a first position for both clockwise and counter clockwise rotation of the motor or a second position for both clockwise and counter clockwise rotation of the motor, the third means for transmitting engaging the first means for transmitting in the first position and engaging the second means for transmitting in the second position.

17. The transmission device of claim 16 , further comprising means for urging the means for retaining into and out of engagement with the means for rotating.